1. Field of the Invention
The present invention relates to a recording medium adapted for use in recording with an aqueous ink and a producing method therefore, and more particularly to an ink recording medium having an image storage property over a prolonged period and a method for producing an ink recording medium capable of securely realizing such characteristics.
2. Related Background Art
The ink jet recording method is to record an image or a character by causing a small droplet of a recording liquid such as an ink to fly by various operating principles and to adhere on a recording medium such as paper, and has features of high-speed, low noise, easy formation of a color image, wide adaptability to various recording patterns and absence of an image development step, thus becoming rapidly popular not only in a printer but also as an output unit for information equipment such as a copying machine, a word processor, a facsimile, and a plotter. Also a digital camera, a digital video camera, a scanner etc. of a high performance are recently made available inexpensively, and, in combination with the pervasiveness of personal computers, printers utilizing the ink jet recording method are becoming very advantageously employed for outputting image information obtained from such instruments. Based on such background, it is being required to output an image comparable in quality to a silver halide photograph or a lithographic multi-color printing, handily by the ink jet recording method.
In order to meet such requirement, improvements on the structure of the printer itself and the recording method are being made to achieve higher recording speed, higher definition, full-color image formation etc., and improvements are also being made on the structure and the characteristics of the recording media.
The recording medium employed in the ink jet recording has conventionally been proposed in various forms. A recording medium, comparable in quality to the silver halide photograph, requires an image formation with an excellent color developing property of dyes, high surface glossiness, high image resolving ability, etc. As a material for constituting an ink-receiving layer of a recording medium capable of providing an image comparable to a silver halide photograph, there can be employed for example alumina hydrate which is described for example in Japanese Patent Application Laid-open No. H07-232475.
Also a storage property is recently required for the recorded image. There is proposed a method of improving the storage property of the recorded image by including a colorant deterioration preventing agent in order to improve light fastness and gas resistance.
For example, in order to resolve a migration phenomenon in which a colorant in the recorded image migrates depending on temperature or humidity to cause a bleeding of the image, there is proposed a recording sheet containing a cationic compound. Also for improving the storage property of the image against light, Japanese Patent Publication No. 4-34512 proposes a recording medium in which a hindered amine compound is added in the form of an acid salt in a coating liquid (for forming an ink-jet recording paper), and Japanese Patent Application Laid-open No. H03-13376 discloses a recording medium coated with a hindered amine and a hindered phenol dissolved in an organic solvent. The recording medium containing such colorant deterioration preventing agent shows an effect to a certain degree in the gas resistance or the light fastness, but is often unsatisfactory on the image storage property over a prolonged period.
The prior art level is described in Japanese Patent Application Laid-open No. 2001-162928. According to the description therein, for an ink-receiving layer of a thickness of 35 μm provided on a film, an upper portion of 5 μm (a portion between the surface and 5 μm deep) and a lower portion of 5 μm (a portion between the interface to the film and upper 5 μm thick from the interface) thereof are crushed, and amounts of nitric acid group contained therein are compared. Result of comparison shows that the amount of the nitric acid group is smaller in the lower 5 μm than in the upper 5 μm, but the effect is limited to a “light fastness” obtained by the presence of the nitric acid group. Stated differently the effect is limited to an effectiveness in comparison to a comparative example which is completely free from the nitric acid groups. Besides, this reference describes applying a large amount of a coating liquid on a recording medium, but does not teach how the material that supplies the nitric acid group is absorbed in the ink-receiving layer or how the drying of the ink-receiving layer after application of the coating liquid is conducted. In addition, the reference does not disclose even a detecting method for the nitric acid group, so that even a repeated test is not possible. In particular, the distribution condition of the nitric acid group in the ink-receiving layer region between the upper portion of 5 μm and the lower portion of 5 μm is not known at all.
Also, Japanese Patent Application Laid-open No. 2000-211246 discloses a recording medium in which aluminum nitrate is internally added and homogeneously dispersed. Japanese Patent Application Laid-open No. 2000-211246 describes that a recording medium containing aluminum nitrate is excellent in light fastness. In the comparison of the light fastness described in Japanese Patent Application Laid-open Nos. 2001-162928 and 2000-211246, though a direct comparison is difficult due to a difference in the test methods, since the light fastness in the comparative example of Japanese Patent Application Laid-open No. 2001-162928 is an acceptable level in Japanese Patent Application Laid-open No. 2000-211246. it is estimated that the example shown in Japanese Patent Application Laid-open No. 2001-162928 has a light fastness weaker than that of the recording medium of Japanese Patent Application Laid-open No. 2000-211246 in which aluminum nitrate is internally added and uniformly dispersed. This fact supports an assumption that the aforementioned 25 μm intermediate range is uniform.
On the other hand, Japanese Patent Application Laid-open No. 2001-010214 discloses an ink-receiving layer of three-layered structure containing a specified nitrogen compound uniformly and formed by applying coating liquids respectively containing silica, polyvinyl alcohol and boric acid by 70 μm each.